Many ceramics and composites are sintered to reduce porosity and to enhance properties of the material such as strength, electrical conductivity, translucency, thermal conductivity, and heat capacity. However, many sintering processes involve the application of high temperatures, typically above 1,000° C., to densify and improve the properties of the material. The use of high temperatures precludes the fabrication of certain types of materials and adds to the expense of fabricating the material or devices. In addition, co-sintering of multi-material systems is difficult due to the differences in thermal stability, shrinkage temperature onsets and rates, and the physical and chemical incompatibilities of the components at high temperatures.
Certain low temperature processes for sintering ceramic are known and can address some of the issues related to high temperature sintering. For example, Ultra Low Temperature Cofired Ceramics (ULTCC) are fired between 450° C. and 750° C. See for example, He et al., “Low-Temperature Sintering Li2MoO4/Ni0.5Zn0.5Fe2O4 Magneto-Dielectric Composites for High-Frequency Application”, J. Am. Ceram. Soc. 2014:97(8):1-5. Also Kahari et al. describe improving the dielectric properties of Li2MoO4 by moistening water-soluble Li2MoO4 powder, compressing it, and post processing the samples at 120° C. See Kahari et al., J. Am. Ceram. Soc. 2015:98(3):687-689. Kahari discloses the particle size of its powders were less than 180 microns but that smaller particle sizes complicates the even moistening of the powders resulting in clay-like clusters, non-uniform density, warpage and cracking and that a large particle size is advantageous. Still others prepare ceramics by combining reaction components to synthesize the ceramic at low temperatures. See, e.g., U.S. Pat. No. 8,313,802. Such preparations take long periods of time lasing several hours to days to produce dense ceramics.
However, a continuing need exists for low temperature processes for sintering ceramics and composites.